dependencies: numpy, matplotlib

[Emmanuelle Gouillart]

> That's a very valid point.  And since it's so little effort to remain
> 1.5 compatible, there seems little reason not to.

> I'm the guilty party that suggested the use of a numpy 1.6 call in the
> converter functions--sorry about that!  Chris has kindly made a PR to
> address the issue.

And it works like a charm, as I just tested with my "old" ;-) set-up
(numpy 1.5). Build and tests work fine, the doc builds well, just
perfect! I saw that you've already merged the PR, but I wanted to confirm
that it works fine for me. Thanks Chris, you rock!

> So, let's talk about Matplotlib--can we use version 1 yet?  If not, I
> suggest that we at least copy over 'subplots', because this function
> makes it so much easier to build clean examples.

I think Matplotlib is a smaller issue, since it's only used to build the
doc (am I wrong?), that is, more a developer's than a user's job. And
Matplotlib 1.0.1 is packaged for the latest ubuntu. There is always the
risk that people download an example, try to execute it and are annoyed
by the error they get if they have an older version of matplotlib. If
people start complaining, then we might copy over matplotlib's subplots
and call skimage.subplots. But I think that this wouldn't discourage new
users, contrary to installation problems. Maybe a sentence in the user
guide on how to adapt examples for matplotlib < 1.0 could help, too. So
my opinion is, yes, we could use version 1 now.

Cheers,
Emmanuelle